Injection molding is often used for molding small plastic articles, such as components for electrical connectors. In a typical rotary injection molding press, a series of mold blocks are mounted in a circumferential manner on a rotatable platform or table. An injection mechanism is fed with solid plastic, usually in pellet form. The injection mechanism typically heats the plastic into a semi-fluid state and a reciprocating screw element forces the semi-fluid plastic under pressure through an injector nozzle into the cavity of a properly positioned mold block. The mold blocks are typically formed having a bottom or base portion secured to the rotatable platform and a hinged top portion that can be opened to remove the molded plastic article from the mold cavity.
In operation of a typical molding apparatus, an opened mold block is positioned in a preparation station where components can be inserted into the mold block and the mold block is closed. The closed mold block is then positioned, by indexing, in an injection station. In the injection station, the reciprocating screw is engaged and the mold block is injected with the semi-fluid plastic. After a mold block has been filled with plastic, the platform is indexed to position the next mold block under the injection mechanism. As the platform is rotated in this indexing fashion, the previous mold block is positioned at a curing station where the fluid plastic within the mold cavity is allowed to heat and harden to form the desired plastic article.
The platform is then indexed to an eject station where the hinged mold is opened and the molded plastic article is removed from the mold block. This indexed rotation of the mold blocks on the rotatable platform continues, thus resembling a circular assembly line for molding plastic articles.
One common problem associated with rotary injection molding is that of how to control the speed and positioning, e.g., indexing, of the rotatable platform. This, consequently, results in a potential inability to immediately stop the rotatable platform upon a predetermined stop signal.
In a typical injection molding apparatus, the drive motor drives the rotatable platform through a series of belts and/or gears. The drive assembly thus provides indirect drive of the turntable. Although such an arrangement has worked sufficiently for known apparatus, after a "break-in" period, the drive assemblies often require readjustment in order to assure that the mold blocks are correctly positioned at their respective stations during operation. Additionally, although such indirect drive assemblies function well, there exists the possibility that even after receipt of a stop signal, the platform may continue to rotate a small, incremental amount, which can result in equipment damage and/or personnel hazards.
Accordingly, there continues to be a need for a rotary injection molding press that incorporates a direct drive arrangement for driving or rotating the rotatable platform. Such a drive arrangement provides precise, direct control of platform movement, and reduces or eliminates post "break-in" maintenance and adjustment of the press drive system.